Curable organopolysiloxane compositions can be used in manufacturing optical devices, such as light guiding devices, protective coatings of semiconductor elements, LED encapsulations, etc. Organopolysiloxane compositions cured via hydrosilylation reaction have better heat stability and light stability than those of epoxy systems. Because of their high transparency and high hardness as well as their adhesion to various substrates upon being cured, intensive researches have been conducted on curable organopolysiloxane compositions.
CN100491470C describes a composition of addition-crosslinking siloxane resin comprising (1) 100 parts by weight of a polyorganosiloxane represented by formula R1aR2bR3cSiO(4-a-b-c)/2 (I); (2) 50-200 parts by weight of a polyorganosiloxane represented by formula R1dH2eR3fSiO(4-d-e-f)/2 (II); or (3) 200 parts by weight of the polyorganosiloxane of the general formula of R1gR2hR3iHkSiO(4-g-h-i-k)/2 (III), which may be used instead of components (1) and (2); (4) 1-100 parts by weight of an alkenyl-rich polyorganosiloxane represented by formula R1lR2mR3nSiO(4-l-m-n)/2 (IV); and (5) 1-100 parts by weight of a hydrogen-rich polyorganosiloxane represented by formula R1oHpR3qSiO4-o-p-g)/2 (V), which may be used additionally or instead of component (4); and (6) a sufficient amount of catalyst.
EP1424363A1 describes a transparent product having heat stability and discoloration resistance, which is obtained by curing of (A) a silicone resin containing at least two vinyl groups directly bonded to silicon atoms in one molecule; (B) an organohydrosilane or hydropolysilane containing at least two hydrogen atoms directly bonded to silicon atoms in one molecule; with (C) a catalyst for hydrosilylation. This composition comprises the following essential components: a component containing silicon-vinyl groups, a crosslinking agent containing Si—H, and a catalyst. It is used in LED devices for the protection, encapsulation, bonding, wavelength alteration or adjustment, and lens formation.
US20070249790A1 discloses a colorless and transparent polysiloxane lens prepared by thermally curing a silicone resin composition. The silicone resin composition contains (A) an organopolysiloxane having a resin structure comprising R1SiO1.5 unit, R22SiO unit and R3aR4bSiO(4-a-b)/2 unit, wherein R1, R2 and R3 independently are methyl, ethyl, propyl, cyclohexyl or phenyl group, R4 is vinyl or allyl group, a is 0, 1 or 2, b is 1 or 2, a+b is 2 or 3, and the number of R22SiO unit is 5-300, (B) an organohydropolysiloxane having a resin structure comprising R1SiO1.5 unit, R22SiO unit and R3cHdSiO(4-c-d)/2 unit, wherein c is 0, 1 or 2, d is 1 or 2, and c+d is 2 or 3, and the number of R22SiO unit is 5-300, and (C) a platinum-based catalyst. A polysiloxane lens having good flexibility, transparency and plasticity with low surface tackiness was provided.
CN100363428C discloses a LED encapsulating composition, which comprises: polyorganosiloxane components (A) and (B), including at least one polyorganosiloxane, and the average composition of the mixture of polyorganosiloxanes is represented by (R1R2R3SiO1/2)M.(R4R5SiO2/2)D.(R6SiO3/2)T.(SiO4/2)Q, wherein R1 to R6 are identical or different groups selected from the group consisting of organic groups, hydroxyl group and hydrogen atom, and at least one of R1 to R6 is a hydrocarbon group with a multiple bond and/or a hydrogen atom, M, D, T and Q each represent a number ranging from 0 to less than 1, M+D+T+Q=1, and Q+T>0; (C) effective amount of a catalyst for addition reaction. The document describes a composition comprising a mixture of several silicon-vinyl components and several Si—H components.
From the above documents, there can be seen a trend of using complex combinations of various components when hardness and transparency are needed. However, the complexity of compositions, especially the complexity of the silicon-vinyl components in curable organopolysiloxane compositions results in extremely high costs and complicated manufacturing processes effecting fluctuant viscosity within the final products.